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1968년 ~ 2024년까지 1,211 건의 한국천문학회지를 격월간 확인하실 수 있습니다.
- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,211건 (DB Construction : 1,211 Articles)
총 게시글 1,211건
페이지 79/122
781
- KIM YONGCHEOL
- Journal of the Korean astronomical society = 천문학회지
- 31, n.2
- pp.77-87
- 1998
- 원문 바로보기
The accumulated knowledge of the influence of solar granulation on spectral lines, i.e. their asymmetry, provides a key to analyze stellar spectral line asymmetries. In this paper, a simple line synthesis using a simple 'model' of granulation was calculated. By adjusting the properties of the granule model, the observed imprints of convection on spectral lines can be reproduced. Since we depict convective flows using a continuous function rather than using a few components of flows (cf. Gray and Toner 1985, 1986; dravins 1990), we were able to identify which components of convection are important in line bisector shapes. The results of this study can be summarized as follows: Firstly, the intensity contrast (i.e. temperature fluctuation), and the area coverage of up- and down-flows are the two important factors which determine the line bisector shapes. Secondly, on the contrary to the assumption of other studies, the effect of horizontal flows is non-negligible. This exercise provides a qualitative understanding of the effect of convection on spectral lines. This knowledge serves as a guideline for understanding the characteristic difference in convection for stars on either side of the 'Granulation Boundary' (Gray 1982; Gray and Nagel 1989).
782
- PARK CHANGBOM
- Journal of the Korean astronomical society = 천문학회지
- 31, n.2
- pp.105-108
- 1998
- 원문 바로보기
We have found that the two-point correlation function of the APM clusters of galaxies has an amplitude much higher than that claimed by the APM group. As the richness limit increases from R = 53 to 80, the correlation length increases from 17.5 to 28.9 <TEX>$h^{-1}Mpc$</TEX>. This indicates that the richness dependence of the APM cluster correlation function is also much stronger than what the APM group has reported. The richness dependence can be represented by a fitting formula ro = 0.53dc + 0.01, which is consistent with the Bahcall's formula ro = 0.4dc. We have tried to find the possible reason for discrepancies. However, our estimates for the APM cluster correlation function are found to be robust against variation of the method of calculation and of sample definition.
783
- KIM SANG CHUL
- Journal of the Korean astronomical society = 천문학회지
- 31, n.1
- pp.51-65
- 1998
- 원문 바로보기
We present B VRI CCD surface photometry for the central <TEX>$(6'.35\times6'.35)$</TEX> regions of the dwarf elliptical galaxies NGC 185 and NGC 205 in the Local Group. Surface brightness profiles of NGC 185 (R<225') and NGC 205 (R<186') show excess components in the central regions. The colors of NGC 185 get bluer inward at R<25', while they remain constant at <TEX>$R\geq25'$</TEX>. The colors of NGC 205 get bluer inward at 1'<R<50', and remain flat outside. Our photometry, supplemented by the photometry based on the far-ultraviolet and visual images of the HST archive data, shows that there is an inversion of color at the very nucleus region (at about 1'). The implications of the redder color of the core part of the nucleus compared with neighboring regions are discussed. The amount of the excess components in the central regions of these galaxies is estimated to be <TEX>$\approx10^5\; L_\bigodot$</TEX>. Distributions of dust clouds in the central regions of the two galaxies are also investigated.
784
- CHO DONG HWAN
- Journal of the Korean astronomical society = 천문학회지
- 31, n.1
- pp.67-74
- 1998
- 원문 바로보기
The VI CCD photometry is made for stars in the globular cluster M22 down to <TEX>$V\approx19^m,\;I\approx18^m$</TEX>. In the color-magnitude diagram (CMD), red giant branch (RGB), asymtotic giant branch (AGB) and blue horizontal branch (BHB) are well defined. The luminosity functions (LF) of RGB, AGB and BHB stars are derived, discussing deficient gaps and bumps in the CMD. The anomalously wide RGB seen in the BV photometric system is found to disappear in the VI photometric system.
785
- LEE SANG-GAK
- Journal of the Korean astronomical society = 천문학회지
- 30, n.1
- pp.1-11
- 1997
- 원문 바로보기
Near infrared JHK magnitudes are presented for two hundred two high proper motion stars. We have observed high proper motion stars in the near-infrared bands(JHK) using the COB detector on the Kitt Peak 1.3m, 2.1m and 4m telescopes. The observations and data reduction procedures are described. The infrared color magnitude diagram and color-color diagrams for the program stars are presented.
786
- PARK CHANGBOM
- Journal of the Korean astronomical society = 천문학회지
- 30, n.1
- pp.83-94
- 1997
- 원문 바로보기
We have identified the candidates for the primordial galaxies in the process of formation in the Hubble Deep Field (hereafter HDF). In order to select these objects we have removed objects brighter than 29-th magnitude in the HDF images and smoothed the maps with the Gaussian filters with the FWHM of 0.8' and 4' to obtain the difference maps. This has enabled us to find. very faint diffuse structures close to the sky level. Peaks are identified in the difference map for each of three HDF chips with three filters (F450W, F606W, and F814W). They have the apparent AB magnitudes typically between 29 and 31. The objects identified in different wavelengths filters have a strong cross-correlations. The correlation lengths are about 0.8'. This means that an object found in one filter can be also found as a peak within 0.8' separation in another filter, thus telling the reality of the identified objects. This angular scale is also the size of the primordial galaxies which have strong color fluctuations on their surfaces. Their large-scale distribution quite resembles that of nearby galaxies, supporting the idea that these objects are ancestors of the present bright galaxies forming at statistically high density regions. Inspections on individual objects show that these primordial galaxy candidates have tiny multiple glares embedded in diffuse backgrounds. Their radial light distributions are quite different from that of nearby bright galaxies. We may be now looking at the epoch of galaxy formation.
787
- JUNG JAE HOON
- Journal of the Korean astronomical society = 천문학회지
- 30, n.1
- pp.71-81
- 1997
- 원문 바로보기
We have studied the IR properties of molecular clouds in the region of the supershell GS234-02 using IRAS and COBE data. The mean values of dust color temperature and optical depth at <TEX>$240{\mu}m$</TEX> are derived to be <TEX>$15.4\pm1.5K\; and\;9.0\pm5.7\times10^{-4}$</TEX>, respectively, which agree well with those determined by Sodroski et al.(1994) for the outer Galaxy. Mean IRAS colors, <TEX>$R_{12}/100= 0.074,\; R_{25}/100= 0.052,\; R_{60/100}= 0.219$</TEX>, indicate that the abundance of PAHs is enhanced but other particles are nearly the same as those of the solar neighborhood. We found the anticorrelation between <TEX>$R_{100/140}\;and\;R_{140/240}$</TEX>. It cannot be explained by the thermal emission of traditional big grains. The anticorrelation implies that, at high ISRF, <TEX>$T_{100/140}$</TEX> underestimates the equilibrium temperature, while <TEX>$T_{140/240}$</TEX> overestimates it and, at low ISRF, vice versa. Therefore we propose to use the intensity ratio, <TEX>$R_{100/240}$</TEX> as a dust thermometer.
788
- LYO A-RAN
- Journal of the Korean astronomical society = 천문학회지
- 30, n.1
- pp.27-70
- 1997
- 원문 바로보기
The brightest stars in galaxies have been used as distance indicators since Hubble. However, the accuracy of the brightest stars for distance estimates has been controversial. Recently, Rozanski & Rowan-Robinson [1994 : MNRAS, 271, 530] argued large errors of this method for the distance determination : 0.58 mag and 0.90 mag, respectively, for the brightest red stars and the brightest blue stars, while Karachentsev & Tikhonov [1994 : A&A, 286, 718] suggested much smaller errors in the distance determination than the former: 0.37 mag for the brightest red stars and 0.46 mag for the brightest blue stars. The reasons for these conflicting results are not yet known. In this study we have investigated the accuracy of this method using a sample of 17 galaxies for which Cepheid distances are known and reliable photometry of the brightest stars are available. We have obtained the calibrations of the relations between the mean luminosities of the three blue and red brightest supergiants (BSGs and RSGs, respectively) and the total luminosities of the parent galaxies: <TEX>$<M_{v(3)RSG}>= 0.21M_B^T- 3.84, \sigma(M_v) = 0.37 mag,\;and\;\delta_{\mu0}=0.47$</TEX> mag for the brightest red supergiants, and <TEX>$<M_{B(3)BSG}>= 0.30M_B^T -3.02, \sigma(M_B)\;=\;0.55 mag,\;and\; \delta_{\mu0}=0.79mag$</TEX> for the brightest blue supergiants. Also it is found that the errors in the distance determination are reduced by a factor of two, as the observing wavelengths increase from B-band to K-band. In conclusion, the brightest red supergiants are considered to be useful for determining the distances to resolved late-type galaxies.
789
- OH K. S.
- Journal of the Korean astronomical society = 천문학회지
- 30, n.1
- pp.95-106
- 1997
- 원문 바로보기
We investigate the velocity distribution of dark matter in the disk of a galaxy like the Milky Way at the solar radius. Using N-body simulations with the total mass and z-component of angular momentum conserved, we calculate the response of a dissipationless dark matter galactic halo during the dissipational collapse of the baryonic matter in spiral galaxy formation. The initial distribution of dark matter and baryonic particles is assumed to be a homogeneous mixture based on a King model. The baryonic matter is assumed to contract, forming the final luminous components of the galaxy, namely the disk and, in some cases, a bulge and central point. Both slow and fast growth of the luminous components are considered. We find that the velocity distribution of dark matter particles in a reference frame rotating slowly about the galaxy center in the plane of the disk is similar to a Maxwellian, but it is somewhat boxier, being flatter at the peak and truncated in the tails of the distribution. We tabulate parameters for the best-fitting Maxwellian and modified-Maxwellian distributions. There is no significant difference between slow collapse and fast collapse for all these results. We were unable to detect any effect of disk formation on the z-dependence of the dark matter density distribution.
790
- CHOE SEUNG-URN
- Journal of the Korean astronomical society = 천문학회지
- 30, n.1
- pp.13-25
- 1997
- 원문 바로보기
Sobolev approximation can be adopted to a macroscopic supersonic motion comparatively larger than a random (thermal) one. It has recently been applied not only to the winds of hot early type stars, but also to envelopes of late type giants and/or supergiants. However, since the ratio of wind velocity to stochastic one is comparatively small in the winds of these stars, the condition for applying the Sobolev approximation is not fulfilled any more. Therefore the validity of the Sobolev approximation must be checked. We have calculated exact P Cygni profiles with various velocity ratios, <TEX>$V_\infty/V_{sto}$</TEX>, using the accelerated lambda iteration method, comparing with those obtained by the Sobolev approximation. While the velocity ratio decrease, serious deviations have been occured over the whole line profile. When the gradual increase in the velocity structure happens near the surface of star, the amount of deviations become more serious even at the high velocity ratios. The investigations have been applied to observed UV line profile of CIV in the Copernicus spectrums <TEX>$of\;\zeta\;Puppis\;and\;NV\;of\;\tau\;Sco$</TEX>. In case of <TEX>$\tau$</TEX> Sco which has an expanding envelope with the gradual velocity increase in the inner region, The Sobolev approximation has given the serious deviations in the line profiles.